Non-volatile memory with extended error correction protection

ABSTRACT

Embodiments of the present disclosure provide methods and apparatuses related to NVM devices with extended error correction protection. In some embodiments, a parity cache is used to store parity values of data values stored in a plurality of codewords of an NVM device. Other embodiments may be described and claimed.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation application of U.S. application Ser.No. 12/427,706, filed Apr. 21, 2009, the entirety of which isincorporated by reference herein.

FIELD OF THE INVENTION

Embodiments of the present disclosure relate to the field of memory, andmore particularly, to non-volatile memory (NVM) with extended errorcorrection protection.

BACKGROUND

Error correction code (ECC) is widely utilized to reflect data valuesstored in NVM devices to avoid read errors. Parity is one of the commonECC protection schemes. For an NVM device, a set of data cells and itscorresponding parity cells is called a codeword.

For NVM devices that can only be programmed uni-directionally, such asflash memories, a series of data values may be written into data cellsof a codeword within a programming cycle, however, parity cell(s) of thecodeword may not be programmed correspondingly without any interveningerase operations. This is because a subsequent write operation normallyrequires at least one state of the parity cell(s) of the codeword to bereversely programmed which cannot be achieved by unidirectionallyprogrammed NVM devices. So, currently when data cells in a codeword areprogrammed for a second time, the parity cells have to be disabled toavoid errors caused by unmatched parity values.

For NVM devices that can be programmed bi-directionally, such as phasechange memories (PGM), the parity cells in a codeword have to beprogrammed every time when a data is written into the codeword, whichmay cause reliability problems of the parity cells.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments will be readily understood by the following detaileddescription in conjunction with the accompanying drawings. To facilitatethis description, like reference numerals designate like structuralelements. Embodiments are illustrated by way of example and not by wayof limitation in the figures of the accompanying drawings.

FIG. 1 illustrates a situation before writing one or more data into aNVM device with extended ECC protection in accordance with anembodiment;

FIG. 2 illustrates a situation after writing the one or more data intothe NVM device with extended ECC protection in accordance with anembodiment;

FIG. 3 illustrates a situation before flushing a parity value from aparity cache to the NVM device in accordance with an embodiment;

FIG. 4 illustrates a situation after flushing the parity value from aparity cache to the NVM device in accordance with an embodiment;

FIG. 5 illustrates a method for operating a NVM device with extended ECCprotection in accordance with an embodiment; and

FIG. 6 illustrates a host device incorporating an NVM device withextended ECC protection in accordance with an embodiment.

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying drawings which form a part hereof wherein like numeralsdesignate like parts throughout, and in which is shown by way ofillustration embodiments in which the disclosure may be practiced. It isto be understood that other embodiments may be utilized and structuralor logical changes may be made without departing from the scope of thepresent disclosure. Therefore, the following detailed description is notto be taken in a limiting sense, and the scope of embodiments inaccordance with the present disclosure is defined by the appended claimsand their equivalents.

Various operations may be described as multiple discrete operations inturn, in a manner that may be helpful in understanding embodiments ofthe present disclosure; however, the order of description should not beconstrued to imply that these operations are order dependent.

For the purposes of the present disclosure, the phrase “A and/or B”means “(A), (B), or (A and B).” For the purposes of the presentdisclosure, the phrase “A, B, and/or C” means “(A), (B), (C), (A and B),(A and C), (B and C), or (A, B and C).”

Various logic blocks may be introduced and described in terms of anoperation provided by the blocks. These logic blocks may includehardware, software, and/or firmware elements in order to provide thedescribed operations. While some of these logic blocks may be shown witha level of specificity, e.g., providing discrete elements in a setarrangement, other embodiments may employ various modifications ofelements/arrangements in order to provide the associated operationswithin the constraints/objectives of a particular embodiment.

The description may use the phrases “in an embodiment,” or “inembodiments,” which may each refer to one or more of the same ordifferent embodiments. Furthermore, the terms “comprising,” “including,”“having,” and the like, as used with respect to embodiments of thepresent disclosure, are synonymous.

FIG. 1 and FIG. 2 illustrate the situations before and after one or moredata are written into an NVM device 120 with extended ECC protection inaccordance with one embodiment. In various embodiments, a parity cache160, which may reside in a volatile memory, may be employed tofacilitate the NVM device 120 in extending the ECC protection of datavalues stored in NVM device 120. In one embodiment, the parity cache 160and the NVM device 120 may be included in the same chip.

In one embodiment, the NVM device 120 may comprise M codewords 122,where M is an integer. Each of the codewords 122 may include a pluralityof data cells configured to store a data value and a plurality of paritycells configured to store a parity value corresponding to the data valuestored in the same codeword. Each codeword 122 may also have a parityvalue validity indicator configured to show if the plurality of paritycells of the codeword 122 are enabled or disabled.

In various embodiments, the parity cache 160 may have N cache lines 162,where N is an integer. In one embodiment, integer M may be equal to theinteger N. In one embodiment, M may not be equal to N and the parityvalues of the codewords 122 may be stored in the parity cache 160 onlywhen necessary. The determination of the necessary situations will bedescribed later in this specification.

In various embodiments, each cache line 162 may include an address field170 to store an address value that is associated with the codeword towhich the cache line 162 corresponds. In various embodiments, thecorresponding relationship between the codewords 122 and the cache lines162 may not be fixed. Each cache line 162 may also comprise a cache linevalidity indicator configured to show if the cache line 162 is valid ornot. In various embodiments, each cache line 162 may also include awrite sequence indicator configured to show the relative sequence inwhich all the cache lines were updated.

In various embodiments, as illustrated in FIG. 1, the data cells 124 ofthe codeword 122-1 may have a first data value including a word HHHHstored therein and the data cells 125 of the codeword 122-2 may have nodata stored therein, e.g., they may be in an erase state. A parity valueP1, reflecting the first data value including the word HHHH in datacells 124, may be stored in the cache line 162-1 of the parity cache 160and a parity value validity indicator 128 may be set as “I” to indicatethat the parity cells 126 of the codeword 122-1 is disabled regardlesswhether there is data in the parity cells 126 or not. In one embodiment,the cache line validity indicator 166 may be set as “V” to indicate thatthe cache line 162-1 is valid.

As shown in FIG. 2, the first data value stored in the codeword 122-1may be changed to a second data value through writing another word JJJJinto the data cells 124 of the codeword 122-1. Correspondingly, theparity value P1 stored in the cache line 162-1 may be modified to P1′ toreflect the second data value including words HHHH and JJJJ stored inthe data cells 124. The settings of the parity value validity indicator128 and the cache line validity indicator 166 may be kept unchanged suchthat the parity cells 126 in codeword 122-1 may still be disabled andthe cache line 162-1 may still be shown as valid.

In various embodiments, a word GGGG may be written into the data cells125 of the codeword 122-2. A parity value P2 which reflects the wordGGGG may be written into the cache line 162-2 and the cache linevalidity indicator 167 of the cache line 162-2 may be set to “V” to showthat the cache line 162-2 is valid. The parity value validity indicator129 of the codeword 122-2 may be set to “I” to show that the parity cell127 is disabled.

FIGS. 3 and 4 illustrate the situations before and after a parity valueis flushed out from the parity cache 160 to the NVM device 120 withextended ECC protection in accordance with one embodiment. In variousembodiments, the parity cache 160 may be full and it may be desirablefor one or more parity values to be flushed out from the parity cache160 so that the corresponding one or more cache lines may be overwrittenand used to accommodate one or more new parity values. In variousembodiments, parity values may be flushed out from the parity cache 160under other situations, for example, when a power loss occurs, parityvalues in the parity cache 160 may be flushed out to minimize the lostof parity values. In various embodiments, when one or more of thecodewords 120 are to be erased, the parity values of these codewords maybe flushed out from the parity cache 160 and the parity cells of thesecodewords may be enable to store the flushed-out parity values.

In one embodiment, parity values in cache lines that are least recentlywritten may be flushed out. In another embodiment, parity values to beflushed out from the parity cache 160 may be determined randomly.

As shown in FIG. 3, the cache line validity indicator in each of thecache lines 162 may be set as “V” showing that all cache lines in theparity cache 160 are valid. In one embodiment, a write sequenceindicator may be used to show when a cache line 162 was written relativeto other cache lines so that parity values in the least recently writtencache lines may be flushed out from the parity cache 160. In oneembodiment, as shown in FIG. 3, the value “00” of the write sequenceindicator 169 may indicate that the cache line 162-2 has been the leastrecently written and the parity value P2′ stored therein may be flushedout from the parity cache 160.

In one embodiment, as shown in FIG. 4, the parity value P2′ in the cacheline 162-2 reflecting data value VL2 in codeword 122-2 may be flushedout and be stored in the corresponding parity cells 127 of the codeword122-2 in the NVM device 120. In one embodiment, the cache line validityindicator 167 may be set as “I” to show that the cache line 162-2 is nolonger valid and the parity value validity indicator 129 may be set as“V” to show that the parity cells 127 of the codeword 122-2 in the NVMdevice 120 is enabled. In various embodiments, cache line 122-2 may beoverwritten and used to store a new parity value after the parity valueP2′ is flushed out.

FIG. 5 is a flowchart depicting a method for a controller configured tooperate an NVM device with extended ECC protection within a programmingcycle in accordance with various embodiments. A programming cycle, asused herein, may be a consecutive series of programming iterations upona codeword without an intervening erase operation. A controller, as usedherein, may be any type of controlling device/logic that may implementthe following described operations, and the controller may includefirmware, state machine or microcode, and so forth.

At block 502, a controller may write a data to a codeword of the NVMdevice with extended ECC protection resulting a data value. At block504, the controller may determine if a parity value reflecting the datavalue in the codeword should be written into parity cells of thiscodeword in the NVM device or not.

In various embodiments, this determination at block 504 may be madebased on the number of protected writes W remaining in the programmingcycle that the parity cells of the codeword can be programmed coherentlywith the data cells to reflect a data value stored in the same codeword.In one embodiment, if this number W is lower than a pre-determinedthreshold K, then the parity value may be written to the parity cache,otherwise the parity value may be stored in the parity cells of thecodeword.

In one embodiment, the number W may be determined based at least on thetotal number of times T that the parity cells of the codeword can beunidirectionally programmed in each programming cycle while stillmaintaining the coherency with the data cells, and the number of times Pthat the parity cells of the codeword have been unidirectionallyprogrammed in the programming cycle. In one embodiment, the numbers Pand T may be determined based at least on the number of the parity cellsand the type of the parity cells. In one embodiment, the number P may bedetermined based on the states of the parity cells of the codeword. Inone embodiment, when there is no data existing in the data cells of thecodeword prior to the writing at block 502, the parity value of thefirst written data value may be stored in the parity cells of thecodeword.

In various embodiments, the determination at block 504 may also be basedon the likelihood of the codeword to be re-written. In one embodiment,the likelihood of the codeword to be re-written may be based on the datathat already exist in the codeword prior to block 502. In anotherembodiment, if the data already exist in the codeword is large, forexample 16 bits, then the likelihood of the codeword to be rewritten maybe low, therefore the parity value may be stored in the parity cells.

In various embodiments, the likelihood of the codeword to be re-writtenmay also be based on data that is being written to the codeword. In oneembodiment, when the data that is being written to the codeword issmall, for example 2 bits, the likelihood of the codeword to bere-written may be high, therefore the parity value may be stored in theparity cache. In other embodiments, the determination at block 504 maybe made based on criteria defined by users for different applications.

At block 506, based on the determination made at block 504, thecontroller may write the parity value into the parity cells of thecodeword. In one embodiment, the controller may go back to block 502 towrite a new data to the codeword.

In one embodiment, if it is determined at block 504 that the parityvalue should not be written into the parity cells of the codeword, thecontroller may determine at block 508 if any parity values need to beflushed out from the parity cache. In one embodiment, the determinationmay be made based at least on whether the number of empty cache lines isbelow a pre-determined threshold E, where E is an integer.

In one embodiment, if the number of empty cache lines is larger than thepre-determined threshold E, the controller may go to block 510 to writethe parity value into the parity cache. At block 512, the controller maydisable the parity cells of the corresponding codeword. Then thecontroller may go back to block 502 to write a new data to the codewordagain.

In one embodiment, if at block 508 it is determined that the number ofempty cache lines is smaller than the threshold value E, which means oneor more parity values stored in one or more cache lines may need to beflushed out from the parity cache. At block 514 the controller maysearch for one or more cache lines for flushing. In one embodiment, thecontroller may randomly choose cache lines for flushing. In anotherembodiment, the controller may choose the least recently written cachelines for flushing. The least recently written cache lines may be foundbased at least on the value of the write sequence indicator of eachcache line.

In one embodiment, a least recently written cache line may be locatedand the controller at block 516 may flush the parity value stored inthis least recently written cache line out to the parity cells of acorresponding codeword in the NVM device. This least recently writtencache line with flushed out parity value may be indicated as invalid atblock 518. At block 520, parity cells of the corresponding codeword maybe programmed based on the flushed out parity value and may be enabled.The controller may go to block 510 to overwrite the least written cacheline and write in the parity value that is determined to be written tothe parity cache at block 504.

FIG. 6 illustrates a host device 600 that may host the NVM device 120and parity cache 160 in accordance with some embodiments. The hostdevice 600 may include one or more processors 604; system control logic608 coupled to at least one of the processor(s) 604; system memory 612coupled to the system control logic 608; the NVM device 120 and paritycache 160 coupled to the system control logic 608; and one or morecommunication interface(s) 620 coupled to the system control logic 608.

System control logic 608 for one embodiment may include any suitableinterface controllers to provide for any suitable interface to thecomponents with which it is coupled. The system control logic 608 mayinclude the controller described above to operate the NVM device 120 andthe parity cache 160.

System memory 612 may be used to load and/or store data/instructions,for example, for the host device 600. In some embodiments, the systemmemory 612 may include the parity cache 160. System memory 612 mayinclude any suitable volatile memory, such as, but not limited to,suitable dynamic random access memory (DRAM).

The NVM device 120 may also be used to load and/or storedata/instructions, for example, for the host device 600. The NVM device120 may include any suitable non-volatile memory, such as, but notlimited to, NOR flash memory, NAND flash memory, phase change memory,etc. In some embodiments, system memory 612 may include the parity cache160.

In some embodiments, instructions 624 may, when executed by theprocessor(s) 604, result in the host device 600 and/or the NVM device120 and parity cache 160 performing at least some of the operationsdescribed above. The instructions may be located in the NVM device 120and/or the system memory 612. In some embodiments, the instructions 624may additionally/alternatively be located in the system control logic608.

Communication interface(s) 620 may provide an interface for the hostdevice 600 to communicate over one or more networks and/or with anyother suitable device. Communication interface(s) 620 may include anysuitable hardware and/or firmware. Communication interface(s) 620 forone embodiment may include, for example, a network adapter, a wirelessnetwork adapter, a telephone modem, and/or a wireless modem. Forwireless communications, communication interface(s) 620 for oneembodiment may use one or more antennas.

For one embodiment, at least one of the processor(s) 604 may be packagedtogether with logic for one or more controllers of system control logic608. For one embodiment, at least one processor of the processor(s) 604may be packaged together with logic for one or more controllers ofsystem control logic 608 to form a System in Package (SiP). For oneembodiment, at least one processor of the processor(s) 604 may beintegrated on the same die with logic for one or more controllers ofsystem control logic 608. For one embodiment, at least one processor ofthe processor(s) 604 may be integrated on the same die with logic forone or more controllers of system control logic 608 to form a System onChip (SoC).

In various embodiments, the host device 600 may be a desktop or laptopcomputer, a server, a set-top box, a digital recorder, a game console, apersonal digital assistant, a mobile phone, a digital media player, adigital camera, etc. The host device 700 may have more or lesscomponents and/or different architectures.

Although certain embodiments have been illustrated and described hereinfor purposes of description of the preferred embodiment, it will beappreciated by those of ordinary skill in the art that a wide variety ofalternate and/or equivalent embodiments or implementations calculated toachieve the same purposes may be substituted for the embodiments shownand described without departing from the scope of the presentdisclosure. Similarly, memory devices of the present disclosure may beemployed in host devices having other architectures. This application isintended to cover any adaptations or variations of the embodimentsdiscussed herein. Therefore, it is manifestly intended that embodimentsin accordance with the present disclosure be limited only by the claimsand the equivalents thereof.

What is claimed is:
 1. A method of storing error correction code (ECC),the method comprising: programming a first location of a non-volatilememory to store first data; storing an error correction code in a cachememory, the error correction code corresponding to the first datawritten to the non-volatile memory; and writing the error correctioncode in the non-volatile memory when it is determined that the firstlocation of a non-volatile memory is not likely to be reprogrammed. 2.The method of claim 1, further comprising determining whether the firstlocation of a non-volatile memory is not likely to be reprogrammed basedat least partly on a comparison between a size of the first data beingstored and a threshold value.
 3. The method of claim 2 wherein thethreshold value is between 2 bits and 16 bits.
 4. The method of claim 1,further comprising determining that the first location is likely to bereprogrammed when the data to be written comprises 2 bits or less. 5.The method of claim 1, further comprising determining that the firstlocation is not likely to be reprogrammed when the data to be writtencomprises 16 bits or more.
 6. The method of claim 1, wherein thenon-volatile memory comprises bi-directional memory.
 7. The method ofclaim 1, wherein the non-volatile memory comprises phase change memory(PCM) cells.
 8. An apparatus comprising: a non-volatile memory device tostore codewords, wherein a data portion of a codeword is stored innon-volatile data memory cells, and an error correction code portion ofthe codeword is stored in non-volatile parity memory cells; a paritycache to store error correction code data; and a controller incommunication with both the non-volatile memory device and the paritycache, wherein the controller is configured to: write data to the dataportion of the codeword of the non-volatile data memory cells; determinewhether or not the data portion of the codeword of the non-volatile datamemory cells is likely to be modified; and copy corresponding errorcorrection code data from the parity cache to the error correction codeportion of the codeword of the non-volatile parity memory cells when itis determined that the data portion of the codeword of the non-volatiledata memory cells is not likely to be modified.
 9. The apparatus ofclaim 8 wherein the controller is configured to determine whether or notthe data portion of the codeword of the non-volatile data memory cellsis not likely to be modified based at least partly on a comparisonbetween a size of the data being written to the codeword of thenon-volatile data memory cells and a threshold value.
 10. The apparatusof claim 9 wherein the threshold value is between 2 bits and 16 bits.11. The apparatus of claim 8, wherein the controller is furtherconfigured to determine that the data portion of the codeword is likelyto be modified when the data to be written comprises 2 bits or less. 12.The apparatus of claim 8, wherein the controller is further configuredto determine that the data portion of the codeword is not likely to bemodified when the data to be written comprises 16 bits or more.
 13. Theapparatus of claim 8, wherein the non-volatile memory device comprisesbi-directional memory cells.
 14. The apparatus of claim 8, wherein thenon-volatile memory device comprises phase change memory (PCM) cells.15. A system comprising: a non-volatile memory device to storecodewords, wherein a data portion of a codeword is stored innon-volatile data memory cells, and an error correction code portion ofthe codeword is stored in non-volatile parity memory cells; a paritycache to store error correction code data; a computer program embodiedin a tangible non-transitory computer-readable medium, the computerprogram comprising: program instructions configured to write data to thedata portion of the codeword of the non-volatile data memory cells;program instructions configured to determine whether or not the dataportion of the codeword of the non-volatile data memory cells is likelyto be modified; and program instructions configured to copycorresponding error correction code data from the parity cache to theerror correction code portion of the codeword of the non-volatile paritymemory cells when it is determined that the data portion of the codewordof the non-volatile data memory cells is not likely to be modified; anda controller in communication with both the non-volatile memory deviceand the parity cache, wherein the controller is configured to executeprogram instructions of the computer program.
 16. The system of claim 15wherein the computer program further comprises program instructionsconfigured to determine whether or not the data portion of the codewordof the non-volatile data memory cells is not likely to be modified basedat least partly on a comparison between a size of the data being writtento the codeword of the non-volatile data memory cells and a thresholdvalue.
 17. The system of claim 16 wherein the threshold value is between2 bits and 16 bits.
 18. The system of claim 15, wherein the computerprogram further comprises program instructions configured to determinethat the data portion of the codeword is likely to be modified when thedata to be written comprises 2 bits or less.
 19. The system of claim 15,wherein the computer program further comprises program instructionsconfigured to determine that the data portion of the codeword is notlikely to be modified when the data to be written comprises 16 bits ormore.
 20. The system of claim 15, wherein the non-volatile memory devicecomprises phase change memory (PCM) cells.